I'm getting the following error when installing the zip package:

Warning: require_once(C:\Inetpub\Stessco\libraries\joomla\installer\adapters\sef_ext.php): failed to open stream: No such file or directory in C:\Inetpub\Stessco\libraries\joomla\installer\installer.php on line 216 Fatal error: require_once(): Failed opening required 'C:\Inetpub\Stessco\libraries\joomla\installer\adapters\sef_ext.php' (include_path='.;c:\php\includes') in C:\Inetpub\Stessco\libraries\joomla\installer\installer.php on line 216

I'm installing on Joomla 1.5.15 running VirtueMart 1.1.9.

I can't find sef_ext.php in the installer package is it generated? What is happening, any ideas?

Thanks.